The present invention relates generally to the field of electrosurgery, and, more particularly, to high efficiency surgical devices and methods which use high frequency (RF) electrical power for cutting, bulk removal by vaporization (ablation), coagulation and treatment of tissue in a conductive liquid environment, as well as other forms of tissue treatment such as shrinking, lesion formation, sculpting and thermal treatment with or without externally supplied liquids.
Least invasive surgical techniques have gained significant popularity because of their ability to accomplish outcomes with reduced patient pain and accelerated return of the patient to normal activities. Arthroscopic surgery, in which the intra-articular space is filled with conducting fluid, allows orthopedists to efficiently perform procedures using special purpose instruments designed specifically for arthroscopists. Among these special purpose tools are various manual graspers and biters, powered shaver blades and burs, and electrosurgical devices. Electrosurgical procedures usually require a proper electrosurgical generator, which supplies the Radio Frequency (RF) electrical power, and a proper surgical electrode (also known as an electrosurgical probe). Under appropriate conditions the desired surgical effects are accomplished.
Note: in common terminology and as used herein the term “electrode” may refer to one or more components of an electrosurgical device (such as an active electrode or a return electrode) or to the entire device, as in an “ablator electrode”. Electrosurgical devices may also be referred to as “probes”.
Arthroscopic electrosurgical procedures rely on the application of RF electrical power using an electrode (or probe) for cutting, ablation or coagulation of tissue structures in a joint space which is filled by liquid. Many types of electrosurgical devices can be used, however, they can be divided to two general categories, monopolar devices and bipolar devices. When monopolar electrosurgical devices are used, the RF current generally flows from an exposed active electrode through the patient's body, to a passive, return current electrode that is externally attached to a suitable location on the patient body. In this way the patient's body is part of the return current circuit. When bipolar electrosurgical devices are used, both the active and the return current electrodes are exposed, and are typically positioned in close proximity. The RF current flows from the active electrode to the return electrode through the nearby tissue and conductive fluids. Monopolar and bipolar devices in many fields of electrosurgery operate according to the same principles.
During the last several years, specialized arthroscopic electrosurgical probes called ablators have been developed. Exemplary of these instruments are ArthroWands manufactured by Arthrocare (Sunnyvale, Calif.), VAPR electrodes manufactured by Mitek Products Division of Johnson & Johnson (Westwood, Mass.) and electrodes by Oratec Interventions, Inc. (Menlo Park, Calif.), Stryker Corporation (Kalamazoo, Mich.) and Smith and Nephew Endoscopy (Andover, Mass.). These ablators differ from conventional arthroscopic electrosurgical probes in that they are designed for the bulk removal of tissue by vaporization in a conductive liquid environment rather than for the cutting of tissue or for coagulation of bleeding vessels.
Recently the use of electrosurgery with conductive fluids for urology, gynecology and other procedures is also becoming popular. Previously, mostly non-conductive fluids were used for these applications.
While standard electrodes are capable of ablation their geometries are not efficient for accomplishing this task. During ablation water within the target tissue is vaporized. Because volumes of tissue are vaporized rather than discretely cut out and removed from the surgical site, the power requirements of ablator electrodes are generally higher than those of other arthroscopic electrosurgical electrodes. The geometry and design of the electrode and the characteristics of the RF power supplied to the electrode greatly affect the power required for ablation (vaporization) of tissue. Electrodes with inefficient designs will require higher power levels than those with efficient designs.
During electrosurgery procedures in conductive fluids, most of the RF energy delivered to an electrode is dissipated in the fluid and in the adjacent tissue as heat, thereby raising the temperature of the fluid within the cavity and of the adjacent tissue. A substantial fraction of the RF power is used for the creation of sparks (arcs) in the vicinity of the electrodes. These sparks accomplish the tissue vaporization, cutting and coagulation. In summary, the sparks are essential for tissue vaporization (ablation), while heating of the liquid and tissue away from the active electrode tip always occurs but has no desirable clinical effect.
The heating of the irrigation fluid and especially the adjacent tissue is not beneficial to the patient. On the contrary, this may substantially increase the likelihood of patient burns. For this and other reasons, improved, efficient electrosurgical electrodes are desirable for tissue vaporization and cutting of tissue structures.
An electrosurgical probe, in general, is composed of a metallic conductor surrounded by a dielectric insulator (for example plastic, ceramic or glass) except for the exposed metallic electrode. The probe electrode is often immersed in a conducting fluid and is brought in contact with the tissue structure during the electrosurgical procedure. The probe is energized, typically at a voltage of few hundred to few thousand volts, using an RF generator operating at a frequency between 100 kHz to over 4 MHz. This voltage induces a current in the conductive liquid and nearby tissue. This current heats the liquid and tissue, the most intense heating occurring in the region very close to the electrode where the current density is highest. At points where the current density is sufficiently high, the liquid boils locally and many steam bubbles are created, the steam bubbles eventually insulating part or all of the electrode. Electrical breakdown in the form of an arc (spark) occurs in the bubbles which insulate the electrode. The sparks in these bubbles are channels of high temperature ionized gas, or plasma (temperature of about a few thousand degrees Kelvin). These high current density sparks, heat, evaporate (ablate) or cut the tissue (depending on the specific surgical procedure and the probe geometry) that is in contact with the spark.
The spark generation and tissue heating, modification or destruction very close to the electrode tip are beneficial and desirable effects. At the same time the induced current heats the liquid and tissue which is a little further away from the immediate vicinity of the electrode tip. This heating is undesirable and potentially dangerous because it may damage tissue structures uncontrollably in surrounding areas and also deep under the surface. The design of higher efficiency probes is desirable as it would lead to less heating of the fluid and tissue not in close proximity, and give the surgeon a larger margin of safety during the procedure.
Ablation (vaporizing) electrodes currently in use, whether monopolar or bipolar, have an active electrode surrounded by an insulator significantly larger in size than the ablating surface of the electrode. For ablators with a circular geometry, the diameter of the portion of the probe which generates ablative arcs (the “working” diameter) is generally not greater than 70 to 80 percent of the diameter of the insulator (the “physical” diameter) and therefore only about 50% of the physical probe area can be considered effective. This increases the size of the distal end of the electrode necessary to achieve a given ablative surface size, and necessitates the use of cannulae with relatively large lumens, an undesirable condition.
It is accordingly an object of this invention to produce an electrosurgical probe which has high efficiency.
It is also an object of this invention to produce an electrosurgical probe which has a distal end of compact size.
These and other objects are accomplished in the invention herein disclosed which is an advanced, high efficiency, electrosurgical probe equipped with an additional one or more metallic electrodes which are not connected directly to any part of power supply circuit. This electrode may contact the surrounding conducting liquid and/or tissue. The potential of this electrode is “floating” and is determined by the size and position of the electrode, the tissue type and properties, and the presence or absence of bodily fluids or externally supplied fluid. This “floating” electrode is mounted in such a way that one portion of the electrode is in close proximity to the probe tip, in the region of high potential. Another portion of the floating electrode is placed further away in a region of otherwise low potential.
The floating electrode generates and concentrates high power density in the vicinity of the active region, and results in more efficient liquid heating, steam bubble formation and bubble trapping in this region. This allows high efficiency operation, which allows the surgeon to substantially decrease the applied RF power and thereby reduce the likelihood of patient burns and injury.
These innovative electrosurgical devices with floating electrodes may be very effective in other medical procedures beyond evaporation (ablation), such as, for instance, for thermal treatments, lesion formation, tissue sculpting, and tissue “drilling”, with or without externally supplied liquids.